JPH03218856A - Thermal head - Google Patents

Abstract

PURPOSE:To improve the bonding properties of a bonding pad in an electrode by employing SiAlON film, SiCeON film or a film consisting of these films laminated as a background layer. CONSTITUTION:A polyimide layer 12 is formed on a base 11 as a heat-resistant resin layer. The thickness of polyimide layer 12 is a few mum to 20mum. An SiAlON film 13 is formed as a background layer on the polyimide layer 12. In order to compensate for the rigidity of a thin resistor formed on the SiAlON film 13 and maintain a required hardness during bonding process such as wire bonding, the SiAlON film 13 should be about 2000Angstrom or larger thick. A resistor 14 is formed on the SiAlON film 12. Electrodes 15, 16 are formed on the resistor 14. A protecting film 18 is formed on an area covering the electrodes 15, 16 and a heating element 17 excepting the bonding pad part of a common electrode 15 and a selected electrode 16. The background layer may be the SiAlON film, SiCeON film or a laminated layer consisting of these films.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermal head used in printers, facsimile machines, and the like.

(Prior Art) As a substrate for a thermal head, a ceramic substrate whose surface is covered with a glassy glaze layer is generally used.

One way to achieve high-speed operation and reduce power consumption with a thermal head, such as by making it compatible with the GIV standard for facsimile, is to provide a heat-resistant resin layer as a heat-insulating layer between the heating resistor and the board. be. As the heat-resistant resin layer, a polyimide resin layer, a polyamide resin layer, a polyamide-imide resin layer, etc. are promising. For example, the thermal conductivity of a polyimide layer is approximately 1/1 that of a glassy glaze layer.
It is 10.

A thermal head having a structure shown in FIG. 5 is being considered as a thermal head provided with a polyimide layer as a heat insulating layer. 1
is an insulating substrate such as a ceramic substrate, the surface of which is covered with a polyimide layer 2. A resistor 3 is formed on the polyimide layer 2, and a common electrode 4 and a selection electrode 5 are formed on the resistor 3. The portion of the resistor exposed from the electrodes 4 and 5 becomes a heating element. 6 is a protective film.

Reference numeral 7 denotes a support plate; an insulating substrate 1 on which a heating element is formed is mounted on the support plate 7, and a printed wiring board 8 is further mounted on the support plate 7.

On the printed wiring board 8 are semiconductor integrated circuit devices for dynamic circuits (sometimes classified into IC, LSI, VLSI, etc., but they are collectively referred to as IC).

The same applies below) 9 is mounted, the drive IC 9 and the selection electrode 5
A wire 10a connects between the drive IC 9 and the wiring of the printed wiring board 8, and a wire 10b connects the drive IC 9 and the wiring of the printed wiring board 8. The common electrode 4 is also connected to wiring on the printed wiring board 8 by a wire (not shown).

In the thermal head shown in Fig. 5, since the polyimide layer 2 exists under the bonding pad portion that connects the wires to the electrodes 4 and 5, it is known that the electrode film peels off during wire bonding, resulting in poor bonding characteristics. ing. In general, wire bonding requires that the electrodes to be connected and their bases have a certain level of hardness. There is a resistor 3 under the electrodes 4 and 5, but the resistor 3
is thin and difficult to ensure sufficient hardness.

This is because the resistance value of the heating element tends to be higher due to the recent demand for lower power consumption, and therefore the thickness of the resistor 3 has to be made thinner.

For this reason, attempts have been made to plate the electrode film, but good results have not been obtained.

Therefore, in order to improve the bonding performance, it is conceivable to form an inorganic insulating film as a base layer on the entire surface between the heat-resistant resin layer and the resistor layer. A thermal head using a SiON film as an inorganic insulating film has been proposed (Japanese Unexamined Patent Publication No. 1988-63).
(Refer to Publication No.-297066).

(Problems to be Solved by the Invention) SiON films have weak adhesion to resin layers such as polyimide resin layers, so when forming a SiON film over a wide area on the resin layer, special It is necessary to perform appropriate treatment.

In the above cited example, surface modification treatment is referred to as plasma treatment, sputter etching treatment, ultraviolet irradiation treatment, ozone gas irradiation treatment, etc. as examples.

The present invention aims to provide a highly reliable thermal head by improving the bonding characteristics of the bonding pads of the electrodes while maintaining good thermal efficiency using a heat-resistant resin layer such as a polyimide resin layer. be.

(Means for Solving the Problems) In the present invention, when providing a base layer over the entire surface between the heat-resistant resin layer and the resistor layer, as the base layer, a SiAlON film,
A SiCeON film or a laminated film of these is used.

Further, in the present invention, a heat-resistant resin layer is selectively formed on a conductive support substrate, a part of the conductor is connected to the support substrate in a portion where the heat-resistant resin layer is not present, and the support substrate is used as a common electrode. Moreover, no heat-resistant resin layer is provided in the bonding portion where the conductor is connected to the signal line, and an inorganic insulating film is provided as a base layer between the conductor and the support substrate in the bonding portion.

(Function) A heat-resistant resin layer such as a polyimide resin layer is formed on the substrate,
SiARON film or SiCeON is applied to the surface of the heat-resistant resin layer.
When forming the base layer of a film, SiA
lON and SiCeON strongly adhere to the heat-resistant resin layer.

The SiAlON film and the SiCeON film are hard inorganic insulating films similar to the SiON film, and improve the bonding properties of the bonding portion of the conductor.

The hardness of the bonding portion can also be ensured by not providing a heat-resistant resin layer in the bonding portion. At this time, when the support substrate is conductive, the base layer of the inorganic insulating film insulates between the conductor of the bonding portion and the support substrate.

(Example) FIG. 1 represents an embodiment.

11 is a substrate, for example a ceramic substrate, a glass plate,
A metal plate or the like can be used. A polyimide layer 12 is formed on the substrate 11 as a heat-resistant resin layer. The thickness of the polyimide layer 12 is approximately several μm to 20 μm. A SiAlON film 13 is formed as a base layer on the polyimide layer 12.
is formed. The SiAlON film 13 supplements the rigidity of the thin resistor formed thereon and maintains the stiffness required during bonding such as wire bonding.
A thickness of about 2,000 people or more, preferably 5,000 people or more is required.

A resistor 14 is formed on the SiAlON film 13. The resistor 14 is made of Ta-Si02 or the like, and its film thickness is about several hundred to three thousand, for example, 500.

Electrodes 15 and 16 are formed on the resistor 14. The electrode 15 is a common electrode connected to all the heating elements 17, and the electrode 16 is a selection electrode connected to each heating element 17 to individually select the heating element 17. As the electrodes 15 and 16, for example, an AQ film or a film in which Au is laminated on NiCr is used, and the thickness thereof is about 8000 to 1 μm. Portion 17 where resistor 14 is exposed between electrodes 15, 16
is a heating element, and the heating elements 17 are arranged in a direction perpendicular to the plane of the drawing.

18 is a protective film made of, for example, Si, N.I. or silicon-alumina nitride. The protective film 18 is formed in a region covering the electrodes 15 and 16 and the heating element 17, except for the bonding pad portion of the common electrode 15 and the bonding pad portion of the selection electrode 16. The thickness of the protective film 18 is approximately 1 to 2 μm.

19 is a support plate, and an insulating substrate 11 on which a heating element is formed.
is mounted on a support plate 19, and a printed wiring board 20 is further mounted on the support plate 19. A drive IC 21 is mounted on the printed wiring board 20, and the rotation I
A wire 22a connects between C21 and the selection electrode 16, and a wire 22b connects between the drive IC 21 and the wiring of the printed wiring board 20. The common electrode 15 is also connected to wiring on the printed wiring board 20 by a wire (not shown).

To explain the method for manufacturing the substrate in the above embodiment, the polyimide resin layer 12 is applied onto the substrate 11 by a coating method or a dipping method, baked, and then the surface of the polyimide resin layer 12 is cleaned with a brush and an organic solvent. do. After that, SiAl is applied as a base layer on the polyimide resin layer 12.
The ON film 13 is formed by a CVD method, a sputtering method, or the like.

In order to examine the bonding performance of the thermal head of the example, a stainless steel substrate was used as the substrate 11, and a polyimide resin layer 12 was formed thereon to a thickness of about 10 μm.

The first sample has a SiAflON film formed on the polyimide resin layer 12 as the base layer 13 to a thickness of about 5,000 mm, and the second sample has a SiAflON film formed on the polyimide resin layer 12 as the base layer 13. An ON film is formed to a thickness of approximately 5000 nm. A heating element, an electrode, and a protective film were formed on each sample substrate by a common thin film thermal head manufacturing process to form a heating substrate of a thermal head. The pretreatment of the surface of the polyimide resin layer 12 before forming the base layer 13 was only brush cleaning and organic solvent cleaning. When we evaluated the bonding performance and reliability of thermal heads using these two types of sample substrates, we found that they had the same characteristics as conventional thermal heads with a glaze layer formed on the surface of a ceramic substrate. .

In the case where the surface of the polyimide resin layer 12 was subjected to special pretreatment such as argon reverse sputtering before forming the base layer 13, the above two types of sample substrates were created and the bonding performance and reliability were similarly evaluated. However, no significant difference was observed between the samples and those without these pretreatments.

A polyimide resin layer is formed on a stainless steel substrate to a thickness of about 10 μm, and a base layer S i A Q is formed on it.
Thermal heads were formed by varying the film thickness of the ON film, and the bonding performance by wire bonding was investigated. The results are shown in the table below.

When the thickness of the base layer is changed to 1,000, 2,000, and 5,000 layers, a defect occurs in which the bonded wire comes off in the 1,000 layer base layer. Even 2,000 people is still not enough, and when it reaches 5,000 people, the bonding performance becomes sufficient.

As a result, the thickness of the base layer needs to be greater than 2,000 layers, preferably 5,000 layers or more.

Next, two types of base layers S i A QO used in the present invention
The adhesion between the N film, the SiCeON film, and other inorganic insulating layers was compared. A destructive test by bending was conducted as a measure of adhesion strength. Therefore, a polyimide resin sheet was used as the heat-resistant resin layer that forms the base layer. After cleaning the polyimide resin sheet by brush cleaning and organic solvent cleaning,
Various underlayers were formed thereon to a thickness of about 10,000 layers. Types of underlayer include SiAlON film, SiCeO
Five types were selected: N film, Sin2 film, Ta20 film, and SiON film. When the polyimide resin sheet is bent so that the base layer is on the outside, a Sin2 film, a Ta20 film,
For the three types of SiON films, destruction occurred when the films were bent 90 degrees. In contrast, the SiAl used in the present invention
The ON film and the SiCeON film did not break even when bent by 180 degrees.

This indicates that the underlayer used in the present invention has excellent adhesion.

In this example, the base layer is a SiAlON film and a SiC
It may be a laminated film of e O N films.

In the embodiment shown in FIG. 1, a polyimide layer 1 is formed on the entire surface of the substrate 11.
2 is formed. The polyimide layer 12 serves as a heat insulating layer for the heating element 17, so it is necessary at the bottom of the heating element 17, but it also serves as a bonding part where bonding is made with the driving IC 21 and a power source for driving the printed wiring board 20. In the bonding part of the common electrode where bonding is made between the wiring for the polyimide layer 12
is not necessary. Rather, it is more convenient for the polyimide layer 12 not to exist in the bonding part in order to improve the reliability of bonding. Therefore, in the embodiment shown in FIG. 1, it is preferable to selectively form the polyimide layer 12 in a region including the lower part of the heating element 17, and in particular not form the polyimide layer 12 in the bonding portion.

In this case, the substrate 11 may be made of a conductive material such as stainless steel or aluminum in addition to a wA#ili material such as ceramic or glass. Since the base layer 13 covers the substrate 11 in areas where the polyimide layer 12 is not present, the base layer 13 serves as an insulator between the resistor 14 and the electrode 16 and the substrate 11 when the substrate 11 is a conductor. act.

FIG. 2 represents another embodiment.

In FIG. 2, a conductive substrate such as stainless steel or aluminum is used as the substrate 30, and by using the substrate 30 as a part of the common electrode, the width of the common electrode on the substrate 30 is narrowed and the width of the thermal head is narrowed. There is.

A polyimide layer 12 is selectively formed on a portion of the conductive substrate 30 that includes a region where the heating element 17 is formed. The polyimide layer 12 covers a portion where the common electrode 15 is connected to the substrate 3o, a portion where the common electrode 15 is connected to wiring of a printed wiring board (not shown), and a lower part of the bonding portion 32 where the selection electrode 16 is connected to the drive IC. is not formed. Reference numeral 31 denotes an inorganic insulating film, which covers the portions of the polyimide layer 12 and the substrate 30 where the polyimide layer 12 is not provided, where the common electrode 15 is connected to the substrate 30 and the common electrode 1.
5 is formed so as to cover the portions of the printed wiring board other than those connected to the wiring. The inorganic insulating film 31 may be SiAΩON or S as in the embodiment shown in FIG.
iCeON is preferable, but in the case of FIG. 2, there is no polyimide layer provided below the bonding part, so
As the inorganic insulating film 31, SiON, SiO2, Si3
N. Various types such as the above can be used. The inorganic insulating film 31 is formed to have a thickness of, for example, several thousand layers or more.

A resistor 14 is formed on the inorganic insulating film 31, as in the embodiment shown in FIG.
6 is formed, and a protective film 18 is formed in a range extending from the heating element 17 to the electrodes 15 and 16.

In FIG. 2, a polyimide layer 12 is selectively formed, and a common electrode 15 is connected to a conductive substrate 3 via a resistor 14.
0, the substrate 30 is used as a part of the common electrode, and even if the width of the common electrode 15 is narrow, sufficient current capacity can be obtained by the substrate 30.

The portion 32 of the selection electrode 16 exposed from the protective film 18 is a bonding portion that is connected to the parking IC by wire bonding or tape carrier method, and the polyimide layer 12 is also formed under the bonding portion 32. The insulation between the conductive substrate 30 and the resistor 14 and the selection electrode 16 is maintained by the inorganic insulating film 31.

The heat generating board in FIG. 2 is also bonded on the support plate 19 in the same way as in FIG.
A connection is made between a part of the board 30 (common electrode lead-out part) and the wiring for the power source for energization of the printed wiring board 20 by a wire or the like.

In the embodiments shown in FIGS. 1 and 2, since the inorganic insulating film 13.31 is present between the heating element 17 and the polyimide layer 12, which is a heat-resistant resin layer, gas is generated from the polyimide layer 12 and generates heat. It does not cause the body 17 to deteriorate.

FIG. 3 shows yet another embodiment.

An aluminum plate 33 is used as the substrate, except for the part where the board 33 is connected to the common electrode 15 and the common electrode extraction part of the board 33 (the part where the connection is made between the wiring of the printed wiring board). An alumite layer 34, which is an insulating layer, is formed on the surface of 33. Alumite layer 34
The thickness is about 0.5 to 2 μm.

A polyimide layer 12 is selectively formed on the surface of the substrate 33 in a region including the lower part of the heat generating section 17 .

A heating element 14 is provided on the substrate 33, 34 and the polyimide layer 12.
is formed, a common electrode 15 and a selection electrode 16 are formed thereon, and a heating element 17 is formed. 18 is a protective film, and the selection electrode 16 exposed from the protective film 18 is a bonding part 32.

In Figure 3, inorganic #i! ! There is no need to separately form an edge film, and by partially anodizing the surface of the aluminum substrate 33, it functions as an inorganic insulating film.

Next, a method for forming the substrate shown in FIG. 3 will be explained with reference to FIG.

(A) A resist pattern 35 is formed on at least the portion of the aluminum plate 33 to be connected to the common electrode 15 and the common electrode extraction portion.

(B) Alumite layer 3 is formed by oxidizing the aluminum substrate 33
form 4.

After that, the resist 35 is removed.

As a method for oxidizing the aluminum substrate, an anodic oxidation method can be used. When the alumite layer 34 is formed by anodic oxidation, a sealing process is performed.

(C) A polyimide layer 12 is selectively formed in a region where a heat generating portion is to be formed. That is, the polyimide layer 12 is not formed in the portion where the common electrode 15 and the substrate 33 are connected, the common electrode extraction portion of the substrate 33, and the bonding portion.

As a method of selectively forming the polyimide layer 12, the polyimide layer is applied to the entire surface of the substrate 33, 34, and then patterned by photolithography and etching to leave the polyimide layer 12 partially.

The polyimide layer 12 may be etched by wet etching or dry etching, but the smaller the angle between the etched edge of the polyimide layer 12 and the substrate, the less the pattern of the electrode formed on the polyimide layer 12 will be cut. It is desirable to select the etching conditions because it is convenient to prevent this. For example, hydrazine is used as the etching agent in wet etching. This allows the angle that the edge of the polyimide layer 12 makes with the substrate to be 45 degrees or less.

As another method for selectively forming the polyimide layer l2,
For example, there are a screen printing method and a method of patterning by photolithography using photosensitive polyimide, and the polyimide layer 12 may be formed by these methods.

Note that the selective formation of the polyimide layer 12 in FIG. 2 can be performed in the same manner.

In FIG. 3, a resistor film is formed over the entire surface of the polyimide layer 12 and substrates 33 and 34 by sputtering, an electrode film is formed over the entire surface of the resistor film, and then patterned by photolithography and etching. to form the heating element and electrodes. At this time, before forming the resistor film, it is preferable to perform reverse sputtering to activate the surface of the polyimide layer 12 in order to improve the adhesion between the resistor film and the polyimide layer 12.

As shown in FIG. 2, wire bonding of the bonding portion of a heat generating substrate in which a polyimide layer is not formed in the bonding portion and an inorganic insulating film 31 is formed between the bonding portion and the substrate 3o;
Comparing wire bonding in which a polyimide layer is also formed at the bottom of the bonding part as shown in Fig. 5, and measuring the bonding strength of both, it is found that in the case of wire bonding in the embodiment shown in Fig. 2, wire bonding The average load required to cut is 9.2g, and the maximum load is 11g,
The minimum load was 6.4g, whereas in the case of wire bonding in Figure 5, the average load to cut the wire decreased to 4.1g, the maximum was 7.9g, and the minimum load was almost no load. The result was that it was not possible. This shows that the reliability of bonding is improved by not forming a polyimide layer in the bonding part.

As the heat-resistant resin layer, a polyamide resin layer or a polyamide-imide resin layer can also be used in addition to the polyimide resin layer shown in the examples.

(Effect of the invention) In a thermal head in which a heating element and electrodes are formed on a heat-resistant resin layer such as a polyimide resin layer via an underlayer, a SiAρON film or a SiCeON film is used as the underlayer. When forming a SiC e O N film, the base layer has sufficient adhesion with the heat-resistant resin layer, even without special pretreatment such as plasma treatment on the heat-resistant resin layer underneath, and the base layer has sufficient adhesion to the base layer. It is possible to obtain a thermal head that does not cause deterioration of the heating element formed therein and has excellent bonding properties at the bonding portion.

Further, in the present invention, the reliability of bonding is also improved by not providing a heat-resistant resin layer below the bonding part.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment, FIGS. 2 and 3 are sectional views showing other embodiments, and FIG. 4 is a process sectional view showing a method for manufacturing the substrate of the embodiment shown in FIG. 3. It is. FIG. 5 is a sectional view showing a conventional thermal head. 11...Substrate, 12...Polyimide resin layer, l3...SiAρON film, 14...
...Resistor, 15, 16... Electrode, 17...
... Heating element, 30 ... Conductive substrate, 31 ...
... Inorganic insulating film, 32 ... Bonding part, 3
3... Aluminum substrate, 34... Alumite layer.

Claims (2)

[Claims] (1) A heat-resistant resin layer is formed on a support substrate, a base layer is formed on this heat-resistant resin layer, and a large number of heating elements and conductors connected to these heat-generating bodies are formed on this base layer,
In the thermal head in which a protective film is formed on at least the heating element, the base layer is a SiAlON film,
A thermal head comprising a SiCeON film or a laminated film thereof. (2) A heat-resistant resin layer is formed on the conductive support substrate, and a large number of heating elements and conductors connected to these heating elements are formed on the heat-resistant resin layer directly or through a base layer, and at least the above-mentioned In the thermal head in which a protective film is formed on the heating element, the heat-resistant resin layer is selectively formed on the support substrate, and a portion of the conductor is attached to the support substrate in a portion where the heat-resistant resin layer is not present. There is also no heat-resistant resin layer in the bonding part where the conductor is connected to the signal line and the support substrate is used as a common electrode, and the conductor in the bonding part and the support substrate are inorganic. A thermal head characterized in that an insulating film is formed as a base layer.